Transparent electro-thermal films are usually electroplated with a transparent conductor layer, on top of which electrodes are placed. The electrodes form on two parallel metal strips, as shown in FIG. 1, one connected to a positive voltage input and the other connected to a negative voltage input, such that a current flowing through the conductor layer generates heat. When materials with a high sheet resistance are used as the conductor layer, the supply voltage has also to be high in order to achieve required heating effect. This affects portability and is potentially unsafe. Moreover, although increasing the thickness of the conductor layer may lower the supply voltage, it causes high manufacturing costs and lowers productivity and device transparency.
Some transparent electro-thermal films may not achieve low input power by using new materials or patterned electrodes, and have to use multiple (5-6) layers of conductor layers. Moreover, heating in such films may not be evenly distributed, having a temperature variance of more than 60K on the same device. These factors may prevent such films from having any practical use.